Armored vehicles are frequently threatened by improvised explosive devices (IEDs) designed to cause harm to the vehicle and its occupants. IEDs are typically one or more grouped artillery shells redeployed and detonated in an effort to inflict casualties. These explosive devices when detonated beneath a floor of a vehicle, often create localized deformation of the floor of the vehicle thereby transmitting large vertical loads onto the lower extremities of occupants of the vehicle. For example, detonations below the underbelly of an armored vehicle may cause the vehicle floor to accelerate at 100 G or more and reach velocities of 7 to 12 m/s over a time period of 3 to 5 msec. These high rates of acceleration and velocity transmit large mechanical forces on the lower extremities of the occupants within the vehicle cabin, often resulting in catastrophic injury or worse.
Armor countermeasures typically consist of heavy metal plates placed between the threat and the vehicle in such a way as to resist hull breach and aggressive floor accelerations. These heavy metal plates also work in concert with layers of additional metal, ceramic, composite or plastic materials designed to prevent lethal high velocity fragments from entering the vehicle. The heavy metal plates are typically mounted to the underside of the vehicle in shapes to take advantage of venting efficiency, inherent geometric stiffness, and deflection characteristics when presented with incoming pressure and fragmentation. Carrying a heavy blast and fragment resistant hulls results in significant performance disadvantage to the vehicle in terms of reduced fuel economy, lost cargo capacity and increased transportation shipping costs.
In addition to the outer metal plates, the interior of the personnel cabin may include a blast mat. During a blast event on an armored vehicle, the lower extremities of the occupants of the vehicle are frequently subjected to injuries from the blast energy being transmitted through the vehicle structure. One current solution to dissipate the energy is to use blast mats where the occupants of the vehicle rest their feet. However, current blast mats are expensive and heavy, often contributing unwanted additional weight to an already heavy vehicle.
Therefore, there is a need for an efficient, cost-effective energy absorbing structures and systems for use during a high acceleration event, such as a blast event underneath the vehicle. The present structures and system are usable, for example, in a personnel cabin of a vehicle, specifically as an interior structure or floor, and includes an energy absorbing structure for absorbing and dissipating the blast forces from an explosive device, thereby lessening the impact of the forces on the lower extremities of the occupants of the vehicle. One such blast absorbing structure includes a stepped floor design, having a bottom section and side sections incorporating a plurality of steps or ridges. In another embodiment, the blast absorbing structure includes a blast abatement structure assembly having an expandable-style floor plate. Energy absorbing supports may also be used in connection with the blast absorbing structures creating a “floating floor” to improve the absorption and dissipation of forces exerted on the underbelly of the vehicle during a blast event, while avoiding the negative tradeoffs of alternative designs.